Add Swagger With NSwag for Your ASP.NET Core API

Nowadays, a good API should provide documentation, and there are different tools to succeed in it. A swagger is a tool that was created to help us prepare documentation for our API and allows consumers to try and start using it efficiently.

Let’s clarify what the difference between OpenAPI and Swagger is?

OpenAPI is a standard format to define structure and syntax REST APIs

A swagger is a tool that allows the implementation of OpenAPI.

For .net developers, two packages provide the functionality to build the documentation:

• NSwag
• Swashbuckle

In this article, we will look at the basic configuration for one of them called NSwag. They both have pretty similar structures. And both of them generate documentation relying on API code. As developers, we don`t need to do anything else except writing well-known code for your API endpoints. Providing a proper configuration is enough, and NSwag will pick up all info directly from controllers.

Initial setup

First, what you need to add is the NuGet package:


dotnet add package NSwag.AspNetCore


After installing the package, let`s configure swagger documentation. In the Startup file, we have to add swagger documentation service to the, and we need to call AddSwaggerDocument with proper configuration.

The main parameters which we need to specify are:

Title — title for the swagger document

Version — allows specifying documentation`s version

Commonly, an authorization mechanism protects API, and the swagger tool allows you to specify how authorization will be provided and allows you to set it up.

DocumentProcessors — gives the ability to provide security tokens in request. We need to add SecurityDefinitionAppender in code to achieve it.

The final version will look like this:

cs
services.AddSwaggerDocument(document => {
document.Title = "Project API";
document.Version = "v1";
document.DocumentProcessors.Add(
new SecurityDefinitionAppender("JWT Token", new OpenApiSecurityScheme
{
Type = OpenApiSecuritySchemeType.ApiKey,
Description = "JWT Token",
Name = "Authorization",
In = OpenApiSecurityApiKeyLocation.Header
})
);
document.OperationProcessors.Add(new OperationSecurityScopeProcessor("JWT Token"));
});


The next step will be to configure ApplicationBuilder to use OpenAPI and UI:

`cs
OpenApiSchema[] schemes = new[] {
OpenApiSchema.Http,
OpenApiSchema.Https
};

app.UseOpenApi(s => {
s.Path = "api/swagger/{documentName}/swagger.json";
s.PostProcess = (document, request) => { document.Schemes = schemes; };
});
app.UseSwaggerUi3(s => {
s.DocumentPath = "api/swagger/{documentName}/swagger.json";
s.Path = $"/api/swagger/ui";
});
`

Conclusion

It`s pretty simple to configure swagger documentation for API and provide convenient UI for consumers who will use it. When you start a new project, try to give a convenient way for consumers to call your API, and swagger will be a good choice.

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